Method And Device For Charging A Stratified Thermal Energy Store

ABSTRACT

A method and a device for charging a stratified thermal energy store are disclosed. According to the method, a working fluid of a heat pump is introduced in the gaseous phase into a liquid heat transfer medium of the stratified thermal energy store at at least one introduction point and is brought into direct physical contact with the heat transfer medium, the pressure in the stratified thermal energy store at the introduction point being greater than or equal to the condensation pressure of the working fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of InternationalApplication No. PCT/EP2015/051130 filed Jan. 21, 2015, which designatesthe United States of America, and claims priority to DE Application No.10 2014 202 849.3 filed Feb. 17, 2014, the contents of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method and a device for charging a stratifiedthermal energy store.

BACKGROUND

Stratified thermal energy stores make it possible to uncouple the timeat which energy is generated from that at which it is used. Inparticular with fluctuating energy sources such as regenerative energytypes, an uncoupling of the times of this kind provides security of thesupply of energy, in particular of electrical energy. Stratified thermalenergy stores can be coupled to heat pumps that pump thermal energy(heat) from a cold to a hot reservoir, the stratified thermal energystore, taking up electrical energy. By using a stratified thermal energystore that is coupled to a heat pump, it is thus possible to uncouplethe time of generating thermal energy from the time of discharging it toa heat consumer, as a result of which for example peak loads in energydemand can be compensated, with the result that the security of supplyimproves overall.

Typically, a stratified thermal energy store is charged with heat bymeans of a heat pump. Here, the heat is transferred to the stratifiedthermal energy store through walls of a heat exchanger. To secure thetransport of heat from the heat pump to the stratified thermal energystore, certain temperature differences are required as the driving forcefor the transport of heat. At the same time, said temperaturedifferences limit the temperature of the heat that can be taken from thestratified store, that is to say its utilizable value. Furthermore, aconstructional space that is not utilizable for storing thermal energymust be provided for the heat transfer surfaces of a heat exchanger.

A stratified thermal energy store having a heat exchanger which has heattransfer surfaces is charged by means of the heat pump in that a workingfluid of the heat pump takes up heat at a low temperature on the primaryside and, within the heat exchanger, on the secondary side transfers theheat of the working fluid at a relatively high temperature to a heatcarrier of the stratified thermal energy store (secondary side).

It is known from the prior art, for taking up heat, to conduct the heatcarrier of the stratified thermal energy store through a condenser onthe secondary side, wherein this condenser is thermally coupled to theheat pump. It is further known from the prior art to guide the workingfluid of the heat pump through a condenser on the secondary side,wherein this condenser is located within the stratified thermal energystore and is in thermal contact with the heat carrier of the stratifiedthermal energy store. In other words, the heat from the heat pump isalways transferred to the stratified thermal energy store through acondenser in which condensation of the working fluid of the heat pumptakes place, wherein the condenser is located outside the stratifiedthermal energy store in the first-mentioned case and within thestratified thermal energy store in the second-mentioned case and isalways in thermal contact with the heat carrier of the stratifiedthermal energy store.

For efficient transfer of the heat from the working fluid to the heatcarrier, the condensers of the prior art have heat transfer surfacesoccupying a large space, which on the one hand require a largeconstructional space and on the other hand reduce the economic benefitof the stratified thermal energy store as a result of high investmentcosts.

SUMMARY

One embodiment provides a method for charging a stratified thermalenergy store, in which a working fluid of a heat pump is introduced inthe gaseous state into a liquid heat carrier of the stratified thermalenergy store at at least one point of introduction and is brought intodirect material contact with the heat carrier, wherein the pressure inthe stratified thermal energy store at the point of introduction isgreater than or equal to the condensation pressure of the working fluid.

In one embodiment, working fluid that is condensed in the stratifiedthermal energy store is returned to the heat pump.

In one embodiment, a working fluid is used for which the densitydownstream of condensation in the stratified thermal energy store isgreater than or equal to the density of the heat carrier.

In one embodiment, the working fluid in the liquid state and the heatcarrier are the same fluid.

In one embodiment, the condensation pressure of the working fluid at atemperature of 100° C. is lower than 1 MPa.

In one embodiment, the working fluid includes at least one of thesubstances 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,perfluoromethyl butanone, 1-chloro-3,3,3-trifluoro-1-propene,cis-1,1,1,4,4,4-hexafluoro-2-butene and/or cyclopentane.

In one embodiment, water is used as the working fluid.

In one embodiment, the working fluid, in the liquid state, is notmiscible with the heat carrier.

In one embodiment, the gaseous working fluid is introduced into the heatcarrier by means of a distribution device, wherein the distributiondevice distributes the working fluid homogeneously in a layer of theheat carrier that is at a constant temperature.

In one embodiment, a regulated pressure accumulator is used as thestratified thermal energy store.

In one embodiment, heat from the stratified thermal energy store issupplied to the working fluid before it is introduced into a compressorof the heat pump.

In one embodiment, the heat carrier that has been separated off from anevaporator of the heat pump by means of a droplet separator is returnedto the stratified thermal energy store.

In one embodiment, the heat carrier is conducted to a heat consumer forthe purpose of utilizing its heat, wherein the heat carrier is conductedthrough a separator before it is utilized in the heat consumer.

In one embodiment, a phase change material is used in the stratifiedthermal energy store for storing thermal energy.

Another embodiment provides a device including a stratified thermalenergy store with a liquid heat carrier and a heat pump with a workingfluid, wherein the stratified thermal energy store and the heat pump areconstructed and coupled such that the working fluid is introduced in thegaseous state into the heat carrier at a point of introduction and isbrought into direct material contact with the heat carrier, wherein thepressure of the stratified thermal energy store at the point ofintroduction is greater than or equal to the condensation pressure ofthe working fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

Example aspects and embodiments of the invention are described belowwith reference to the drawings, in which:

FIG. 1 shows a pressure accumulator that is coupled to a heat pump,wherein a working fluid of the heat pump is introduced directly into theheat carrier of the pressure accumulator; and

FIG. 2 shows a hydrostatic pressure accumulator that is coupled to theheat pump, wherein the working fluid of the heat pump is againintroduced directly into the heat carrier of the pressure accumulator.

DETAILED DESCRIPTION

Embodiments of the present invention may provide improved charging of astratified thermal energy store with thermal energy.

Some embodiments provide a method for charging a stratified thermalenergy store, wherein a working fluid of a heat pump is introduced inthe gaseous state into a liquid heat carrier of the stratified thermalenergy store at at least one point of introduction and is brought intodirect material contact with the heat carrier, wherein the pressure inthe stratified thermal energy store at the point of introduction isgreater than or equal to the condensation pressure of the working fluid.

, the working fluid of the heat pump is introduced in the gaseous statedirectly into the liquid heat carrier of the stratified thermal energystore, as a result of which there is a direct material contact betweenthe heat carrier and the working fluid. The direct material contactresults in condensation of the gaseous working fluid. This is the casebecause the pressure in the stratified thermal energy store at the pointof introduction of the gaseous working fluid, or in a partial region ofthe stratified thermal energy store at which the gaseous working fluidis introduced, is greater than or equal to the condensation pressure ofthe working fluid. The condensation pressure of the working fluid heredepends on the temperature at the point of introduction, and should beadjusted according to said temperature. The term “condensation pressure”means the pressure at which the gaseous working fluid of the heat pumpchanges from the gaseous to the liquid state, namely the temperaturethat is present at the point of introduction of the working fluid in thestratified store. In other words, the condensation point of the gaseousworking fluid is reached at the point of introduction, or in a partialregion of the stratified thermal energy store. As a result of the directmaterial contact between the gaseous working fluid and the liquid heatcarrier of the stratified thermal energy store, and the consequentcondensation of the working fluid, the condensation heat that isreleased in the process of condensation of the working fluid istransferred directly to the heat carrier of the stratified thermalenergy store. Additional condensers, heat exchangers and/or heattransfer surfaces are thus dispensed with. As a result of the inventivedispensing with condensers, heat exchangers and/or heat transfersurfaces, additional losses of thermal energy in and/or on saidcomponents can be avoided, as a result of which the efficiency of thestratified thermal energy store is increased.

A further advantage of the direct material contact between the gaseousworking fluid and the liquid heat carrier of the stratified thermalenergy store is that there is no need for large temperature differencesbetween the working fluid and the heat carrier for efficient transfer ofheat. If the stratified thermal energy store is charged by means of aheat pump having a compressor, an initial pressure at the compressor mayconsequently be reduced, as a result of which the consumption ofelectrical energy by the heat pump is advantageously reduced.

The disclosed device for charging a stratified thermal energy storeincludes a stratified thermal energy store with a liquid heat carrierand a heat pump with a working fluid, wherein the stratified thermalenergy store and the heat pump are constructed and coupled such that theworking fluid is introduced in the gaseous state (as superheated vaporor as saturated vapor) into the heat carrier at a point of introductionand is brought into direct material contact with the heat carrier,wherein the pressure of the stratified thermal energy store at the pointof introduction is greater than or equal to the condensation pressure ofthe working fluid.

The disclosed device enables a direct material contact between thegaseous and consequently also the condensed (liquid) working fluid andthe liquid heat carrier. This gives like and equivalent advantages tothose of the method according to the invention that has already beendescribed.

In a further embodiment of the method, the working fluid that iscondensed in the stratified thermal energy store is returned to the heatpump.

By returning the condensed and thus liquid working fluid, a particularlyadvantageous circulation process for charging the stratified thermalenergy store is made possible. It may be provided, before it is returnedto the working cycle of the heat pump, for the condensed working fluidto be conducted through a separator, which separates residues of theheat carrier that are present in the condensed working fluid, with theresult that no or almost no heat carrier is discharged into the workingcycle of the heat pump. The material separation of working fluid andheat carrier that is to be performed downstream of condensation of theworking fluid is not restricted to the use of a separator, and may beperformed using devices that are known from the prior art and/orequivalents thereof.

According to an embodiment of the method, there is used a working fluidwhereof the density downstream of condensation in the stratified thermalenergy store is greater than or equal to the density of the heatcarrier, wherein a density that is really greater at all times may bepreferred.

The density of the condensed working fluid that is greater than that ofthe liquid heat carrier has the advantage that the working fluid can beintroduced or put close to the upper end of the stratified thermalenergy store. As a result of the action of gravity prevailing at thelocation of the stratified thermal energy store, the working fluid,which is denser than the heat carrier, will fall during and/or after itscondensation, from the point of introduction to a lower end of thestratified thermal energy store. In this context, the relative terms“upper” and “lower”, as is known, relate to the prevailing direction ofgravity. Typically, the heat carrier in the stratified thermal energystore will have the highest temperature at the upper end thereof.

The advantage of the greater density of the condensed working fluid andthe resulting fall of the working fluid is that the working fluid issubcooled to the temperature of the stratified thermal energy storeprevailing at the lower end, as a result of which the heat carrier andconsequently the stratified thermal energy store are charged withadditional heat.

It is a further advantage that the condensed working fluid is almostcompletely condensed by the fall and the associated constant materialcontact with the heat carrier. After the condensed working fluid hasfallen and accumulated at the lower end of the stratified thermal energystore, for example at the base, it can be returned from there back tothe heat pump.

In an embodiment, one and the same fluid is used for the working fluidin the liquid state and the liquid heat carrier.

Advantageously, as a result additional separators that separate theworking fluid from the heat carrier, for example before it is returnedto the heat pump or to a heat consumer, can be dispensed with.

In a further embodiment, there is used a working fluid that, at atemperature of 100° C. (373.15 K), has a condensation pressure lowerthan 1 MPa.

Working fluids that, at a temperature of 100° C., have a condensationpressure lower than 1 MPa are called low-pressure fluids here. Anadvantage of such low-pressure fluids is the fact that, in combinationwith known stratified thermal energy stores, they make it possible touse the disclosed method. This is the case because stratified thermalenergy stores that are typical in the prior art, in particularstratified stores using water, are at a pressure lower than 1 MPa and inparticular in the range from 0.3 MPa to 1 MPa. Typical working fluidsthat are used in heat pumps, such as the fluids R134a, R400c or R410a,have a condensation pressure in the range from 2 MPa to 4 MPa at 100° C.The condensation pressure of said working fluids is thus significantlygreater than the pressure that typically prevails in stratified thermalenergy stores, with the result that when the working fluid is introducedat a temperature of 100° C. no condensation of the working fluid occurs.Low-pressure fluids, by contrast, have a condensation pressure that isin the range of pressures that prevail in stratified stores, with theresult that they condense when they are in contact with the liquid heatcarrier of the stratified thermal energy store.

In some embodiments, the working fluid includes at least one of thesubstances 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone(trade name Novec™ 649), perfluoromethyl butanone,1-chloro-3,3,3-trifluoro-1-propene, cis-1,1,1,4,4,4-hexafluoro-2-buteneand/or cyclopentane.

In some embodiments, said substances may be used in combination withstratified thermal energy stores that are known from the prior art. Forexample, at a temperature of 100° C. Novec™ 649 has a condensationpressure of 0.45 MPa, perfluoromethyl butanone a condensation pressureof 0.89 MPa and cyclopentane a condensation pressure of 0.42 MPa. At100° C., therefore, the condensation pressure of said fluids issignificantly below the condensation pressure of, for example, R134a,which has a condensation pressure of around 3.97 MPa.

A further advantage of said substances is their ease of technicalhandling. They are characterized by good environmental compatibility andby their properties relating to safety, such as a lack of flammabilityand a very low greenhouse gas potential. In general, the substancesNovec™ 649 and perfluoromethyl butanone are allocated to the substanceclass of fluoroketones, while cyclopentane is allocated to the substanceclass of cycloalkanes.

According to a further embodiment of the method, water is used as theworking fluid.

As a result, advantageously additional separators that are able toseparate the working fluid from the heat carrier can be dispensed with.In the case of hydrostatic stratified thermal energy stores, which buildup the pressure in the stratified thermal energy store solely by way ofthe hydrostatic pressure of the water column, the height of the point ofintroduction of the working fluid into the heat carrier is therefore notsignificant. In particular, the stratified store using water may becharged at its upper end with the introduced gaseous and subsequentlycondensed working fluid, as a result of which advantageously there isonly a small time lag between charging the stratified store that useswater and reaching the temperature that is desired at the upper end.

In a further embodiment of the method, there is used a working fluidthat, in the liquid (condensed) state, is not miscible with the liquidheat carrier.

In other words, the condensed working fluid and the liquid heat carrierform a two-phase liquid, wherein the one phase is formed by thecondensed working fluid and the other phase by the liquid heat carrier.It is also possible to provide a working fluid that has low miscibilitywith the heat carrier in the liquid state.

As a result of the mixture of working fluid and heat carrier beingpresent in two phases, it is possible to perform a material separationof said fluids in a simple manner, in particular if the condensedworking fluid and the liquid heat carrier have different densities. Forexample, the already mentioned low-pressure fluids Novec™ 649,perfluoromethyl butanone and cyclopentane are poorly soluble in water,which is particularly suitable as a heat carrier, and so are onlymiscible with water in small quantities. For example, only 20 ppm ofwater may be dissolved in Novec™ 649.

In a further embodiment, the gaseous working fluid is introduced intothe heat carrier by means of a distribution device, wherein thedistribution device distributes the working fluid homogeneously in alayer of the heat carrier that is at a constant temperature.

Stratified thermal energy stores, such as stratified stores using water,have a layered construction in respect of the temperature of their heatcarrier, wherein each layer has a particular temperature and density. Asregards the efficiency of heat transfer from the working fluid of theheat pump to the heat carrier, it is thus advantageous to distribute thegaseous working fluid uniformly or homogeneously in a layer of the heatcarrier. The terms “uniform” and “homogeneous”, and the temperature ordensity of a layer, are in all cases to be understood as approximate.

Typical stratified stores are oriented vertically—relative to thegravity prevailing at the stratified store—such that the individuallayers of the stratified store extend horizontally. As a result of theuniform distribution of the gaseous working fluid in a layer of theliquid heat carrier, the surface of material contact (contact surface)between the heat carrier and the working fluid is increased, as a resultof which the efficiency of the heat transfer from the working fluid tothe heat carrier is improved.

As a result of uniform distribution of the working fluid in a horizontallayer of the stratified thermal energy store, furthermore a distributionof the pulses of introduced working fluid is made possible, with theresult that undesired mixing procedures that could result in the layersbecoming completely mixed can be prevented.

Possible distribution devices are for example horizontal distributorpipe systems such as are used in stratified stores. In particular, thedistribution devices that are known there result in a reduction in theinput rate of the working fluid into the heat carrier (cf. Göppert etal., Chemie Ingenieur Technik, 2008, 80, No 3). Furthermore, the inputrate of the gaseous working fluid may be regulated by altering thecross-sectional surface area of input holes in the distribution device.A further advantage of regulating the cross-sectional surface areas ofthe input holes is that a primary bubble size of the gaseous workingfluid can be set.

In one embodiment of the method, a regulated pressure accumulator isused as the stratified thermal energy store.

Advantageously, with a regulated pressure accumulator the pressureinside the stratified thermal energy store can be regulated to aparticular pressure range. By regulating the pressure in the pressureaccumulator, the pressure inside the pressure accumulator can beadjusted to the condensation pressure of the working fluid, with theresult that condensation of the working fluid occurs regardless of thetemperature that prevails at the point of introduction. For example, asa result the gaseous working fluid may be introduced at a point ofintroduction in the stratified store that is as high up as possible. Inthis arrangement, the temperature of a layer of the stratified store orpressure accumulator is correlated to the height of the layer, with theresult that a point of introduction that is at the greatest possibleheight corresponds to a greatest possible temperature.

According to a further embodiment of the method, heat from thestratified thermal energy store is supplied to the working fluid beforeit is introduced into a compressor of the heat pump.

This is particularly advantageous if working fluids whereof thecondensation curve has an overhang are used. The heat that is requiredwith such working fluids, which serves to superheat the working fluidbefore it enters the compressor, can thus be taken from the stratifiedthermal energy store.

In a further embodiment, heat carrier that has been separated off froman evaporator of the heat pump by means of a droplet separator isreturned to the stratified thermal energy store.

As a result of the direct material contact of the working fluid with theheat carrier of the stratified thermal energy store, it is in principlenot possible to prevent the heat carrier from being introduced into theworking fluid and thus into a cycle of the working fluid within the heatpump. Thus, liquid heat carrier that has not (also) evaporatedaccumulates in particular in the evaporator of the heat pump. This heatcarrier that accumulates in the evaporator is advantageously removedfrom the evaporator by means of a droplet separator and returned to thestratified thermal energy store.

According to an embodiment, the heat carrier is conducted to a heatconsumer for the purpose of utilizing its heat, wherein the heat carrieris conducted through a separator before it is utilized in the heatconsumer.

Conducting the heat carrier through a separator is provided inparticular when the heat carrier is removed directly from the stratifiedthermal energy store. When the heat carrier is removed directly, as aresult of the inventive material contact between the working fluid andthe heat carrier, some of the working fluid is discharged with the heatcarrier. In this arrangement, the working fluid may be discharged indroplet form (as an emulsion) or indeed as a constituent that isdissolved in the heat carrier (as a solution).

Advantageously, by means of the separator it is ensured that thedischarged portions of the working fluid do not reach the heat consumerand where appropriate may be returned to the stratified thermal energystore and/or the heat pump. Suitable for the separation are for exampleactive droplet separators and/or coalescing separators. A furtherpossibility for preventing working fluid from being discharged is toreduce the solubility of the working fluid in the heat carrier as aresult of the reduced temperature of the heat consumer. This is the casefor substance mixtures that have a higher solubility at highertemperature. As a result of the reduced temperature of the heatconsumer, the working fluid is precipitated and can thus be materiallyseparated from the heat carrier.

In the case of indirect removal of the heat for a heat consumer, forexample by way of a heat exchanger, a separator of this kind that is onthe heat consumer side and separates the working fluid from the heatcarrier may be dispensed with.

According to a further embodiment, a phase change material (PCM) is usedin the stratified thermal energy store for storing thermal energy.

The stratified store thus includes two heat carriers, wherein thefurther heat carrier takes the form of a phase change material.

Phase change materials or phase change stores may be preferred, sincethey can store thermal energy with low losses and with numerous repeatcycles and over a long period of time. In particular, a phase changematerial whereof the melting point (phase change temperature) is lowerthan the condensation point of the working fluid (at condensationpressure) may be preferred. For example, the condensation point of theworking fluid may be 130° C., so a melting point of 125° C. of the phasechange material may be preferred. Thus, a melting point that is at most5% lower than the condensation point may be preferred.

The stratified store may include further heat carriers that are in thesolid state. In this arrangement, the porosity of the solid heatcarriers may be adapted to their purpose. For example, the porosity maybe selected such that it becomes possible to lower the condensed workingfluid, which has a greater density than the liquid heat carrier.

FIG. 1 shows, in a schematic illustration, a regulated pressureaccumulator 2 that is coupled to a heat pump 6 such that the workingfluid 4 of the heat pump 6 is distributed to the heat carrier 10, whichis in direct material contact with the working fluid 12, by way of adistribution device 12 at a height 8 on the pressure accumulator 2.

The heat pump 6 includes a compressor 14, an evaporator 16, an expansionvalve 20, a separator 18, a droplet separator 15 and a nonreturn valve22. The working fluid 4 circulates counterclockwise 36 in the heat pump6.

Further visible in FIG. 1 is an expansion vessel 24, a pump 28, afurther expansion valve 30 and a reservoir 26 for the heat carrier 10.Said components 24, 26, 28, 30 serve to regulate the pressureaccumulator 2 and/or the heat carrier 10. In the exemplary embodimentthat is shown in FIG. 1, water is used as the heat carrier 10.

The gaseous working fluid 4 is introduced into the heat carrier 10downstream of the compressor 14 at the height 8 on the pressureaccumulator 2, by way of the distribution device 12, and is thus broughtinto direct material contact with the heat carrier 10. Here, thetemperature of the pressure accumulator 2 at the introduction height 8is for example 130° C. If for example Novec™ 649 is used as the workingfluid, the pressure in the pressure accumulator 2 must be at least 0.9MPa so that immediate condensation of the gaseous working fluid 4 takesplace.

One advantage of the regulated pressure accumulator 2 is that theworking fluid 4 can be introduced at a point on the pressure accumulator2 that is as hot as possible. This is the case because the condensationpressure of the working fluid 4 at the introduction height 8 can alwaysbe exceeded by adjusting the pressure in the pressure accumulator 2. Ingeneral, the heat from the pressure accumulator 2 is removed for a heatconsumer (which is not shown) at the point of highest possibletemperature. By introducing the working fluid 4 at said point, thepressure accumulator 2 can reach the temperatures required by the heatconsumer efficiently and in little time with a low thermal load.

In the exemplary embodiment that is shown in FIG. 1, there may be usedas the working fluid 4 Novec™ 649, which has a density of around 1300kg/m³. As the heat carrier 10 there is used water 10, which has adensity of 1000 kg/m³, with the result that the working fluid 4 has agreater density than the heat carrier 10. The density of the workingfluid 4, greater than that of the heat carrier 10, causes the workingfluid 4 to fall to the base 9 of the pressure accumulator 2 throughgravity 100. As a result of the working fluid 4 falling to the base 9 ofthe pressure accumulator 2, the working fluid 4 is advantageouslysubcooled until it reaches the temperature of the pressure accumulator 2that prevails at the base 9, with the result that additional heat isremoved from the working fluid 4. Given the low miscibility of Novec™649 and water, there results a phase of the working fluid 4 that isdeposited at the base 9 and can then be removed from the base 9 of thepressure accumulator 2 and returned to the working cycle 36 of the heatpump 6 by way of the separator 18. As a result of the (liquid) separator18, it is ensured that no heat carrier 10 from the pressure accumulator2 is introduced into the working cycle 36 of the heat pump 6.

If a working fluid 4 that has a lower density than water 10 is used, forexample cyclopentane (C₅H₁₀), which has a density of 650 kg/m³, theworking fluid 4 rises after condensation and must thus be removed at anupper end of the pressure accumulator 2.

The nonreturn valve 22 prevents heat carrier 10 from being dischargedinto the compressor 14 and thus into the working cycle 36 of the heatpump 6.

FIG. 2 shows an alternative embodiment of the method according to theinvention, wherein instead of a regulated pressure accumulator 2 ahydrostatic pressure accumulator 3 is used. In this arrangement, theheat pump 6 includes the elements that have already been shown anddiscussed in FIG. 1.

Unlike a pressure accumulator 2, in a hydrostatic pressure accumulator 3the pressure inside the store 3 is generated solely by the hydrostaticpressure of the heat carrier 10, in this case water 10. In other words,the pressure in the pressure accumulator 3 is generated solely by way ofthe liquid column of water 10. If once again Novec™ 649 is introduced asthe working fluid 4 into the hydrostatic pressure accumulator at atemperature of 110° C., a pressure of at least 0.6 MPa is required forthe working fluid 4 to condense. The result of this is that the point ofintroduction or height 8 at which the working fluid 4 is introduced intothe pressure accumulator 3 must be selected such that at least 50 m ofwater 10 lies above the introduction height 8 of the working fluid 4. Ingeneral, the pressure can be selected in accordance with theintroduction height 8 of the working fluid 4.

In order to increase the pressure in the hydrostatic pressureaccumulator 3 further without making the liquid column of the heatcarrier 10 taller or the introduction height 8 lower, a cold water layer32 is placed at the upper end of the pressure accumulator 3. The coldwater layer 32 is separated from the water 10 of the hydrostaticpressure accumulator 3 by a separation device 34. Placing the cold waterlayer 32 at the upper end of the hydrostatic pressure accumulator 3ensures that the pressure at the introduction height 8 exceeds thecondensation pressure of the working fluid 4 as it is introduced, andcondensation of the working fluid 4 occurs. In this way, theintroduction height 8 of the working fluid 4 may be made higher, as aresult of which the temperature at the introduction height 8 may beincreased.

As was already the case in FIG. 1, the working fluid 4 falls to the base9 of the hydrostatic pressure accumulator 3, as a result of its density,which is greater than the heat carrier 10, through the effect of gravity100. From there, it can once again be supplied to the working cycle 36of the heat pump 6 by way of a separator 18. If the heat carrier 10 isdenser than the working fluid 4, removal of the working fluid 4 at anupper end of the hydrostatic pressure accumulator 3 is provided.

Although the invention has been closely illustrated and described indetail by way of the preferred exemplary embodiments, the invention isnot restricted by the disclosed examples, and alternatively othervariations may be derived therefrom by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. A method for charging a stratified thermal energystore, comprising: introducing a working fluid of a heat pump in thegaseous state into a liquid heat carrier of the stratified thermalenergy store at at least one point of introduction; bringing the workingfluid into direct material contact with the heat carrier, wherein thepressure in the stratified thermal energy store at the point ofintroduction is greater than or equal to the condensation pressure ofthe working fluid.
 2. The method of claim 1, wherein working fluid thatis condensed in the stratified thermal energy store is returned to theheat pump.
 3. The method of claim 1, wherein the density of thecondensed working fluid downstream of condensation in the stratifiedthermal energy store is greater than or equal to the density of the heatcarrier.
 4. The method of claim 1, wherein the working fluid in theliquid state and the heat carrier are the same fluid.
 5. The method ofclaim 1, wherein the condensation pressure of the working fluid at atemperature of 100° C. is lower than 1 MPa.
 6. The method of claim 1,wherein the working fluid includes at least one of the substances1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,perfluoromethyl butanone, 1-chloro-3,3,3-trifluoro-1-propene,cis-1,1,1,4,4,4-hexafluoro-2-butene and/or cyclopentane.
 7. The methodof claim 1, wherein the working fluid is water.
 8. The method of claim1, wherein the working fluid, in the liquid state, is not miscible withthe heat carrier.
 9. The method of claim 1, wherein comprisingintroducing the gaseous working fluid into the heat carrier by adistribution device, wherein the distribution device distributes theworking fluid homogeneously in a layer of the heat carrier that is at aconstant temperature.
 10. The method of claim 1, wherein the stratifiedthermal energy store comprises a regulated pressure accumulator.
 11. Themethod of claim 1, comprising supplying heat from the stratified thermalenergy store to the working fluid before introducing the working fluidinto a compressor of the heat pump.
 12. The method of claim 1, wherein avolume of the heat carrier that has been separated off from anevaporator of the heat pump by a droplet separator is returned to thestratified thermal energy store.
 13. The method of claim 1, wherein theheat carrier is conducted to a heat consumer for, wherein the heatcarrier is conducted through a separator before being utilized by theheat consumer.
 14. The method of claim 1, wherein a phase changematerial is used in the stratified thermal energy store for storingthermal energy.
 15. A device, including: a stratified thermal energystore including a liquid heat carrier, and a heat pump with a workingfluid, wherein the stratified thermal energy store and the heat pump areconfigured and coupled such that the working fluid is introduced in thegaseous state into the heat carrier at a point of introduction and isbrought into direct material contact with the heat carrier, wherein thepressure of the stratified thermal energy store at the point ofintroduction is greater than or equal to the condensation pressure ofthe working fluid.